The Evolved Packet System (EPS) of the 3GPP is composed of the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), the Mobility Management Entity (MME), the Serving Gateway (S-GW), the Packet Data Network Gateway (P-GW) and the Home Subscriber Server (HSS).
The EPS supports the intercommunication with the non-3GPP system (as shown in FIG. 1), wherein, the intercommunication with the non-3GPP system is realized through the S2a/b/c interface, and the P-GW is used as the anchor point between the 3GPP and non-3GPP system. In the system structure diagram of the EPS system, the non-3GPP system access is divided into an untrusted non-3GPP access and a trusted non-3GPP access; wherein, the untrusted non-3GPP access needs to be connected with the P-GW through the Evolved Packet Data Gateway (ePDG), and the interface between the ePDG and the P-GW is S2b; the trusted non-3GPP access can be connected with the P-GW through the S2a interface directly, and the S2a interface performs the information interaction by adopting the PMIP protocol; in addition, the S2c interface provides the control and mobility support related to the user plane between the HE and the P-GW, and the mobility management protocol supported by the S2c interface is the Mobile IPv6 Support for Dual Stack Hosts and Routers (DSMIPv6), which can be used in the untrusted non-3GPP and trusted non-3GPP access.
The Wireless Local Area Network (WLAN) can be regarded as a non-3GPP system access EPS, and this involves the interconnection and intercommunication problem of the mergence of fixed network and mobile network that a lot of operators pay close attention to.
At present, there are a number of studies on the procedure and policy of intercommunication of the S2b and the S2c interfaces, and while the study on the S2a interface is little. In the related art, as shown in FIG. 2, after the UE completes the non-3GPP specific procedure and the extensible authentication protocol (LAP) authorization procedure, the Layer 3 (L3) message is performed between the UE and the trusted non-3GPP IP access network (TNAN) element, and then the trusted non-3GPP IP access network (TNAN) initiates a tunnel establishment procedure to the P-GW of the mobile core network after receiving the L3 message. Here, the L3 message is used as a way to trigger the TNAN and the P-GW to establish the tunnel, however, that message is not clear.